The invention relates to a driving device for an adjusting device of a motor vehicle and to a method for operating a driving device of this kind.
A driving device of this kind for an adjusting device of a motor vehicle comprises a housing or housing section which at least partially encloses components of the driving device and an electric-motor-driven drive shaft which extends in a longitudinal direction and which is axially supported on the housing or housing section at least via one end. In the context of an adjusting device, such a driving device can be used, for example, in the form of a window lifter on a vehicle door or, alternatively, in the form of a seat adjusting system or of a sliding roof actuation system, for example.
In the case of a driving device of this kind, which is known from EP 1 436 880 B1 and which is configured as a drive for a window lifter, a drive shaft is supported axially on a housing of the driving device. Here, support can be provided, for example, by the fact that the drive shaft rests axially against the housing or against a housing section or runs on the housing via a thrust element, e.g. a disk-shaped thrust element, for providing low friction support.
The drive shaft in the case of a conventional driving device has an axial play relative to the housing providing axial support for the drive shaft and, as a rule, this cannot be completely avoided and changes during the operation of the driving device owing to wear. Owing to such axial play, there may be troublesome noise during the operation of the driving device, e.g. when switching the direction of rotation of the driving device and consequently when there is a change in the axial loading direction of the drive shaft (referred to as the “changeover click”). Moreover, the change in the axial play due to wear during operation can also have a disadvantageous effect on the operating behavior of the driving device and can lead to unstable running of the driving device.
In the case of the driving device known from EP 1 436 880 B1, a piezoelectric actuator reaches radially around the drive shaft, said actuator exercising a braking action on the drive shaft of the driving device when, for example, a trapped part is detected at a window pane that is to be adjusted by the window lifter. Axial support is not provided by the actuator described in EP 1 436 880 B1.
GB 1 592 748 B has disclosed a piezoelectric sensor which is arranged at one axial end of a drive shaft and which senses and evaluates axial forces arising at the drive shaft in order to detect trapping at an adjusting device. The drive shaft is supported directly on a housing of the driving device, on the one hand, and via a spring acting on the piezoelectric sensor, on the other hand.